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2.2: The Transport of Substances Across a Cell Membrane

McGraw Hill Section 2.2

Ms. Klodt

on 25 January 2015

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Transcript of 2.2: The Transport of Substances Across a Cell Membrane

The Transport of Substances Across A Cell Membrane
Movement without energy
Follows concentration gradient (high concentration to low concentration)
Requires the use of energy
ATP (adenosine triphosphate)
Breaking off a phosphate group releases energy from the bond
Forms ADP
Moves against the concentration gradient
Movement of large molecules
Using vesicles
Uses energy
Passive Transport
Active Transport
Membrane Assisted Transport
Molecules dissolved in cytoplasm and extracellular fluid
Non-polar so they can move through the hydrophobic layer of the phospholipid bilayer cell membrane
Substances move from a region of high concentration to low concentration
Factors that affect rate of diffusion are
molecule size (smaller increases rate)
molecule polarity (non-polar increases rate)
molecule/ion charge (charged cannot diffuse)
Temperature (higher increases rate)
Pressure (high pressure increases rate)
Diffusion that is helped by a protein embedded in the membrane
Channel proteins: hydrophilic interior for any polar substances to pass through the membrane
Carrier Proteins: bind to specific molecules
Facilitated Diffusion
Movement of water molecules across a semi-permeable membrane
high concentration of solutes in solution = hypertonic
water leaves the cell, causing
animal cells to shrink
plant cells to have the cholorplast in the middle of the cell and loss of cytoplasm
lower concentration of solutes = hypotonic
water enters the cell, causing
animal cells to swell/lyse
plant cells to have turgor pressure and choloroplast move to beside the cell wall
same concentration = isotonic
no net movement of water
Exterior is composed of non-polar amino acids that can bind with the non-polar fatty acids making the interior of the cell membrane
Shape and size of the channel (or tunnel) of the protein determines what molecules can pass through
Can be gated, and closed when necessary, or open all the time
Ions and polar molecules can pass through
Channel Proteins
Bind to specific molecules then carry them through cell membrane
change shape during transportation
transport large molecules
Exterior is made of non-polar amino acids, as with channel proteins
Carrier Proteins
Uses ATP to move substances from one side of a membrane to the other
Sodium Potassium Pump
3 Na+ ions bind to the ion pump
ATP binds and breaks, providing energy and Na+ moves to the outside of the cell
2 K+ ions bind on the outside of the cell
K+ is released to inside of the cell
Primary Active Transport
Uses electrogradient as source of energy
Difference in charge across a membrane
Causes a concentration gradient and an electrical potential
Hydrogen-Sucrose Pump
More H+ ions outside the cell than inside
Sucrose binds to a carrier inside the cell
Hydrogen ions bind on the outside and provide energy to move sucrose
Secondary Active Transport
Cell membrane folds around a substance and then pinches off, forming a vesicle
Moves substances into a cell
Large pieces of organic matter (i.e. bacteria)
Liquid matter with particles in it
Receptor-mediated Endocytosis
Receptor proteins on the outside of the cell, in a coated pit, bind with molecules
Vesicles merge with the cell membrane and push substances from the cell
Can be waste products or cell products (hormones, enzymes, etc.)
Key Terms
passive transport
concentration gradient
facilitated diffusion
channel proteins
carrier proteins
active transport
electrochemical gradient
membrane assisted transport
receptor-mediated endocytosis
Main Ideas
use appropriate terminology related to biochemistry,including, but not limited to: active and passive transport
describe the structure of cell membranes according to the fluid mosaic model, and explain the dynamics of passive transport, facilitated diffusion, and the movement of large particles across the cell membrane by the processes of endocytosis and exocytosis
So, can you?
Explain passive transport?
Describe osmosis, diffusion and facilitated diffusion?
Tell how a concentration gradient works?
Explain active transport?
Describe the function of ATP and how it makes energy?
Compare and contrast primary and secondary active transport?
Explain membrane assisted transportation?
Differentiate between the types of endocystosis?
Show how exocytosis works within the cell?
Full transcript